Investigation of Optical and Radiative Properties of Aerosol over Urban Cities of India

Advancements in anthropogenic activities influence the characteristics of aerosols in the atmosphere. Changes in aerosol type, size, and concentration affect aerosol optical depth (AOD), which can be estimated by studying their variability with regions and seasons. The present study focuses on understanding the optical and radiative properties of aerosol in the visible range (0.4–0.7 μm) using soot, water-soluble, and insoluble components during the winter, pre-monsoon, monsoon, and post-monsoon seasons of a normal rainfall year (2008) over different geographical regions – Delhi, Hyderabad, Ahmedabad, and Dibrugarh, located in four directions of the Indian subcontinent. This study utilized Optical Properties of Aerosols and Clouds (OPAC) and Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART) models. The obtained results show a high annual average of AOD (~0.92) over Delhi, which might be due to a higher concentration of aerosols. Along with this, high extinction coefficient values (~0.16 to 1.09) were also found over Delhi during all the seasons, which show the presence of high concentrations of soot, soluble, and insoluble components. On the other hand, high values of single scattering albedo (SSA) (~0.85 to 0.87, ~0.90 to 0.92, and ~0.88 to 0.90) were observed during winter, pre-monsoon, and monsoon, respectively, over Hyderabad, suggesting more availability of water-soluble and insoluble aerosols in the region. It is inferred that scattering and absorption properties of aerosol vary significantly with season at the regional scale, which can influence direct and indirect effects of aerosol. Such a regional-scale study can estimate changes in optical and radiative properties of aerosol, which can be further utilized as an input in weather models for better predictive outcomes over the cities.